The present invention relates to improvements for use in automatic sample changers and more particularly, relates to apparatus for preventing excessive friction among test tube holders in a turn having a relatively short radius in the track of an automatic sample changer of the type used in the radiopharmaceutical field. The present invention also relates to means to adjust the relative spacing among the test tube holders in the continuous track of such automatic sample changer.
There have recently become available for use by the health professions, automatic systems for performing radiopharmaceutical tests, such as gamma counting. Such tests typically are based upon detecting and determining the level of radioactivity in a test tube. The level of radioactivity may be used in tests where radioactive antibodies are introduced into a laboratory sample, another operation such as washing the sample is performed, and then the amount of radiation remaining in the test tube is measured. Presently, such radioactive tests are used in the detection of hepatitis. It has been known to perform such tests manually, wherein the necessary preliminary operations are performed on a test tube and then the test tube is either irradiated or the radiation of the test tube is measured in a specially shielded location.
The automatic sample changer provides a system whereby the laboratory technician may load the samples into a number of test tubes and insert such test tubes into holders in a track in the machine and then leave the machine unattended to perform the desired test. Examples of such automatic sample changers may be seen in U.S. Pat. Nos. 4,024,395, issued May 17, 1977, and also in 4,001,584, issued Jan. 4, 1977. Automatic sample changers typically employ a plurality of plastic rings or pucks which are adapted to slide along a continuous track. The plastic rings or pucks are provided with a inside diameter which is chosen to accept a standard size test tube. The continuous track is arranged in a serpentine fashion and the test tube holder pucks are positively driven along the track by a driving wheel which contacts the rings. An elevator housing is located along the track such that each puck will pass into the housing. The test tube in that puck will be lowered into a shielded safe chamber and then a counting operation performed. The elevator then returns the test tube and puck to the track and the next succeeding sample is lowered by the elevator.
Needless to say, such automatic sample changers have provided a great improvement in the efficiency of the typical radioactive testing operation. Furthermore, although the original automatic sample changers employ up to 50 pucks or rings, i.e., it was possible to load 50 different radioactive samples into the automatic sample changer and then leave the machine unattended, more recent sample changers have been expanded and enlarged in successive steps to accept 100, 150, 200 and 300 separate and discrete samples in one machine top. As might be expected, the automatic sample changer which is able to accept 300 separate individual test tubes will necessarily require a long continuous track and a relatively large amount of surface area upon which to arrange the track. In order to overcome this requirement for a large surface area, an extremely complex and circuitous serpentine, track arrangement is provided in the top of the automatic sample changer so that the 300 test tube holders may be accomodated on a machine surface of reasonable size. However, in using such complex, circuitous, and convoluted track arrangement, it has been found that in attempting to drive the rings or pucks through particularly sharp turns, that large frictional forces are present between the individual pucks and also between the pucks and the continuous track. Such sharp turns may be likened to switchbacks used by railroads in traversing mountains.
Additionally, in systems utilizing a large quantity of plastic ring sample holders or pucks, it has been found upon relocating the system from one ambient temperature to another, that the rings will necessarily expand or contract. The cumulative effect of 300 rings undergoing such expansion or contraction will obviously affect the spacing between each puck and thereby affect the overall puck train length. The spacing is critical since, as mentioned above, the potential for a large amount of friction to be present between the puck and between the pucks and the track is particularly great when negotiating the many small radius turns along the continuous track.